Can someone explain certain words in context for me?

Question

"I sometimes wonder that we can be so frivolous, I may almost say, as to attend to the gross but somewhat foreign form of servitude called ***** Slavery, there are so many keen and subtle masters that enslave both north and south."

what does GROSS, FOREIGN, and "many keen and subtle masters" mean?

Answer 1

Gross means vulgar or common, foreign means foreign to human nature. Keen and subtle masters refers to economic and societal influences that cause the continuation of slavery, comparing them to the slave owners themselves.

Answer 2

gross - extremely dissatisfying, vulgar

keen - intelligent

subtle- not obvious